The popularity of electronic devices such as personal computers, word processors, video movie cameras and cellular phones in recent years has led to an ever increasing demand for multilayer printed circuit boards. A new feature of multilayer printed circuit boards is the formation of IVH (for example, see Patent document 1) as a type of electrical interlayer connecting means using non-penetrating via holes to increase wiring accommodation and surface mounting density, in order to meet demands for smaller and lighter-weight electronic devices with increased multifunctionality.
The conventional process for production of multilayer printed circuit boards will be explained first. FIG. 10 shows a conventional process for production of a multilayer printed circuit board with IVH. In FIG. 10, 6 is a multilayer printed circuit board, 61a, b are outer layer printed circuit boards, 62a, b are through-holes, 62c, d are copper plating layers, 63a, b are inner layer conductor patterns, 63c is a copper foil, 64 is a prepreg, 65a, b are outer layer conductor patterns, 66a, b are IVHs and 67 is a component hole.
First, an NC drill machine or the like is used to form through-hole perforations in a double-sided copper clad laminate obtained by laminating a copper foil 63c on both sides of a glass cloth base epoxy resin-laminated sheet, and then through-holes 62a, b are formed for electrical connection of both sides by copper plating, and a copper plating layer 62c is formed. A method such as etching is used to form inner layer conductor patterns 63a, b on one each of the sides of outer layer printed circuit boards 61a, b where the through-holes 62a, b and copper plating layer 62c have been formed. This yields surface-oxidized outer layer printed circuit boards 61a, b with through-holes 62a, b and inner layer conductor patterns 63a, b, as shown in FIG. 10(a).
After sandwiching a semi-cured prepreg 64 obtained by impregnating a glass cloth with an epoxy resin or the like between the outer layer printed circuit boards 61a, b, it is situated between a pair of stainless steel plates. The obtained laminate is set between the heating plates of a hot press machine (not shown) and then pressed and heated at a prescribed pressure and temperature for welding lamination of the outer layer printed circuit boards 61a, b and the prepreg 64, to form a multilayer copper clad laminate having inner layer conductor patterns 63a, b on the inner layer, as shown in FIG. 10(b).
After next forming perforations that can function as component holes 67 or mounting holes, copper plating 62e is again carried out to form a copper plating layer 62e on the surfaces of the component holes 67 and copper plating layers 62c, d. An etching resist is formed on the copper plating layer 62e surface by a screen printing method or photographic development method, and then etching is performed and the etching resist is released. This yields a multilayer printed circuit board 6 having formed thereon outer layer conductor patterns 65a, b, conductor-formed IVHs 66a, b and through-holes as component holes 67/mounting holes, as shown in FIG. 10(c).
The prepreg used for manufacture of this type of multilayer printed circuit board may be one as described in Patent document 2, for example.
[Patent document 1] Japanese Unexamined Patent Publication HEI No. 6-268345
[Patent document 2] Japanese Patent Publication No. 2904311